Perchloroethylene (tetrachloroethylene) is a widely used industrial solvent. It is used extensively as a degreasing solvent, particularly in vapor phase degreasing where the article to be cleaned is suspended over a boiling sump of perchloroethylene and the suspended article is cleaned by condensation of perchloroethylene vapors on its surface. Perchloroethylene tends to decompose in the presence of oxygen, heat, light, metals, metal salts, organic materials and other contaminants to which it is exposed during storage and use in degreasing operations. Decomposition of perchloroethylene adversely affects its desirable properties as well as its useful life as a solvent.
It is known that the decomposition of perchloroethylene can be minimized or prevented by the addition of small quantities of various chemical components which act as stabilizers. These components are often combinations of two or more different types of chemical compounds and are known as stabilizer systems. For example, the acid materials produced as a result of the decomposition reaction can be bound by the use of agents such as amines, and oxidation reactions can be retarded by phenols, so these types of materials are often added in combination. The epoxide compounds, such as epichlorohydrin, glycidol, glycidyl ethers and the like, have also been widely used in the most effective perchloroethylene stabilizer systems. The epoxides are compounds incorporating the oxirane structure, a three membered ring containing one oxygen atom and two carbon atoms.
Epichlorohydrin is the most commonly used epoxide compound due to its ready availability and proven effectiveness in stabilizer systems. However, epichlorohydrin has been demonstrated to exhibit mutagenic activity. The continued use of epoxide compounds in perchloroethylene stabilization has therefore become questionable, and the development of an effective stabilizer system which is free of epoxides would be desirable.